1. Field of the Invention
The present invention is related generally to beverage dispensing systems employing a cooling subsystem, and more particularly to a chilling glycol circulation system incorporated in a cold plate for a beverage dispensing system.
2. Description of Related Art
In a large number of restaurants, taverns, pubs, and clubs where beer is sold at a bar, beer kegs are stored in a cold room where they can be maintained at a reduced temperature along with other perishable food items and beverages. These cold rooms are typically maintained at a temperature of approximately 40° F. The beer is conducted from the cold rooms to serving towers at the bar through plastic tubes or beer lines that extend within a thermally insulated jacket, or trunk line. The distance between the cold room and the tower can be as little as fifteen feet and as great as two hundred feet, depending on the layout of the particular establishment. To move the beer through the lines, such systems require a pressurization subsystem that forces the beer from the cold room down the length of beer line to the beer tower for dispensing. The pressurization subsystem introduces a gas such as nitrogen or carbon dioxide into the beverage, pressurizing the beverage to enable it to be pumped through the beer lines.
As the beer is communicated from the cold room to the dispensing tower, it gains heat from the ambient atmosphere and warms to a temperature above the original 40° F. Even enveloped in the thermally insulated trunk line, traveling seventy five feet the beer in the trunk line can result in a beer temperature increase of 8° F. at the end of the trunk line. Thus, where the length of the beer lines from the cold room to the dispensing towers is not minimal, the beer dispensing system will traditionally include one or more refrigerated glycol chillers that incorporate glycol re-circulating lines of plastic tubing that extend within the thermally insulated trunk line carrying the beer lines. The presence of the glycol recirculation lines can reduce the warming of the beer by five to six degrees, resulting in an end temperature as low as 42° F., or a two degree rise from cold room to the end of the trunk line.
The trunk lines may lead to a counter top supporting cabinetry such that their downstream ends terminate below the counter tops, where they connect with balance lines that extend from the down stream end of the trunk line to the delivery tubes adjacent the respective dispensing valve. In practice the beer flowing from the beer lines, through the balance lines and stainless steel tubes can be expected to further warm from 2° F. to 4° F. Accordingly, in the example above beer initially at 40° F. in the cold room is warmed to 42° F. at the downstream end of the trunk line, and further warmed to approximately 45° F. by the time it reaches the dispensing valve.
When beer is charged with a gas such as carbon dioxide to move the beer through the various lines, the gas is entrained in the fluid and resides in a stable state for temperatures below or at approximately 30° F. That is, the gas does not bubble out of the fluid but is carried by the fluid and gives the beverage its distinctive effervescence when consumed. However, as the temperature of the beer rises above 30° F., the gas gradually becomes increasingly unstable and begins to bubble or foam out of the flowing beer. Further warming of the beer increases the foaming effect as the gas bubbles coalesce and propagate downstream, and foaming is further exacerbated by disturbances in the beer such as the turbulence generated when the beer is dispensed from the dispensing valve. When beer is warmed to 45° F. or more, the gas becomes so unstable and so much foam is generated when it is dispensed through the valves that it can often times cannot be served to patrons. As a result, the beer dispensed through the valve must be discarded as waste resulting in significant erosion of the owner's profit.
In the recent past, the purveyors of beer using systems such as that described above have resorted to the inclusion of jacketed heat exchangers in the beer distribution systems just prior to the dispensing valves to chill beer to a low temperature at the down stream end of the trunk lines. The heat exchangers are thermally insulated cast aluminum or aluminum alloy cold plates that incorporate stainless steel tubular beer conducting coils for communicating beer from the downstream end of the trunk lines to the upstream end of the balance lines. Within the cold plates next to the beer conducting coils are a series of coolant re-circulating coils used to remove heat from the beer in a heat exchanger relationship. Typically the coolant used in such systems has been glycol.
The chilled glycol carries heat away from the cold plate and the beer lines within the cold plate in a continuous manner to lower the temperature of the beer entering the balance lines. If the glycol is chilled to, for example, 28° or 29° F. where it enters the cold plate it can be expected that the beer flowing through the cold plate will be chilled to about 29° F. In such case, the beer as it leaves the cold plate will be conducted to the dispensing valve via the balance lines and will be dispensed at about 35° F. At this temperature, the generation of foam can be minimal if attention and care is applied when the delivery is carried out through the dispensing valve and profits can be preserved.
A system such as that described above is disclosed in U.S. Pat. No. 5,694,787, entitled “Counter Top Beer Chilling Dispensing Tower,” issued Dec. 9, 1997 and which the present inventor was a co-inventor. The '787 patent described a glycol recirculating coil unit or basket including elongate tubular glycol inlet and outlet tube sections having upstream ends connected to an upstream manifold and downstream ends connected to a downstream manifold. Between the upstream and downstream manifolds, the stock stainless steel 5/16″ ID tubing is arranged in a serpentine manner with alternating runner portions and recurvate end portions forming the glycol recirculating line. The manifold can divide the flow of the glycol at the upstream side into several smaller lines to increase the surface area and decrease the residency time of the cooling fluid, thereby enhancing the heat exchange properties of the glycol unit. The upstream and downstream manifolds connect to feed and return lines for a glycol chiller apparatus that chill the glycol. The entire teachings and disclosure of the '787 patent are fully incorporated herein by reference. A method of making a cold plate is disclosed in U.S. Pat. No. 5,484,015 to Kyees, entitled “Cold Plate and Method of Making Same,” the disclosure of which is also incorporated fully herein by reference.
The prior art has relied upon a glycol distribution system within the cold plate that has a multi-outlet manifold. It has been discovered the multi-outlet manifold of the glycol heat exchanging unit may not equally distribute the flow of the heat exchange fluid amongst the divided flow streams. For example, where the manifold has a single large inlet centrally disposed and five exiting lines arranged linearly across the manifold as shown, for example, in FIG. 4 of the '787 patent, then it has been discovered that the exiting lines proximal to the manifold inlet receive a higher proportion of the available glycol and the distal or edge exit lines receive a lower percentage of the glycol. This may be a result of the dynamic pressure present at the central outlets as the inlet flow impinges the outlet, that is not present at the distally located outlets. Because the interleaved lines of beer are substantially of the same temperature and flow rate, a disparity in the chilling effectiveness of the glycol lines will result in a disparate chilling effect across the cross section of the chiller. As a result, a beer line occupying a distally disposed position on the upstream manifold may receive less cooling and be delivered at a higher temperature than those beers occupying a more central position on the manifold. This phenomenon leads to inconsistent results and can overchill some beer lines while underchilling others.